The present invention relates to control of brushless permanent magnet motors, more particularly to selective implementation of one of a plurality of motor control schemes to effect an associated stator current waveform profile.
The above-identified copending patent applications describe the challenges of developing efficient electric motor drives for vehicles, as a viable alternative to combustion engines. Electronically controlled pulsed energization of motor windings offers the prospect of more flexible management of motor characteristics. By control of pulse width, duty cycle, and switched application of a battery source to appropriate stator windings, broad functional versatility can be achieved. The use of permanent magnets in conjunction with such windings is advantageous in limiting current consumption.
In a vehicle drive environment, wherein power availability is limited to an on-board supply, it is highly desirable to attain a high torque output capability at minimum power consumption. Motor structural arrangements described in the copending applications contribute to these objectives. As described in those applications, electromagnet core segments may be configured as isolated magnetically permeable structures in an annular ring to provide increased flux concentration. Isolation of the electromagnet core segments permits individual concentration of flux in the magnetic cores, with a minimum of flux loss or deleterious transformer interference effects from interaction other electromagnet members.
The above-identified copending application Ser. No. 10/173,610 describes a control system for a multiphase motor that compensates for variations in individual phase circuit elements. A high degree of precision controllability is obtained with each phase control loop closely matched with its corresponding winding and structure. Successive switched energization of each phase winding is governed by a controller that generates signals in accordance with parameters associated with the respective stator phase components. The phase windings are energized with current of sinusoidal waveform for high efficiency operation. The control system varies the output current to respond to, and accurately track, the user""s torque command input.
The sinusoidal current waveform profile obtained with this commutation strategy can extend battery life through efficient operation. However, in vehicle driving operation there is often the need for torque capability in excess of that available from the most efficient control scheme. Typically, the power supply is rated for a maximum current discharge rate, for example, 10.0 amps. If the user of the system requests a torque command that correlates to this maximum current draw, then the motor torque output for a sinusoidal current waveform profile is limited, for example, to approximately 54.0 Nm in a motor with a configuration such as described above. In vehicle drive applications, torque input commands are associated by users with commands for change of speed. In typical driving operation, user torque requests are subject to wide variability with little, if any, predictability. A driver may demand higher acceleration or greater speed than the system can accommodate at maximum torque with a sinusoidal current waveform. Driving conditions, such as steep uphill grade or heavy vehicle load or the like, may impose other limitations on available speed and acceleration.
The need thus exists for a vehicle motor control system that is capable of performing with high efficiency yet can deliver increased torque output when required by the user.
The present invention fulfills this need by making available a plurality of motor control schemes for a motor drive, each of which can provide a unique current waveform profile. An advantage of the invention is that one of the motor control schemes may be selected to obtain a current waveform profile that has the greatest capability to meet operating objectives. For example, a control scheme may be selected that yields high efficiency operation, such as a sinusoidal waveform, while another control scheme may be selected that provides higher torque, albeit with less operating efficiency.
An additional advantage of the invention is that selection between motor control schemes may be made by the user in accordance with the user""s needs or objectives with respect to torque and efficiency, or other factors, e.g., low torque ripple and noise, etc., at any particular time. In accordance with the motor control schemes selected, control signals are generated to energize the motor winding with current waveform profiles that are associated therewith.
The present invention may be manifested in a control system for a multiphase motor having a plurality of stator phase components, each stator phase component comprising a phase winding formed on a core element, and a permanent magnet rotor. Preferably, each of the stator core elements comprises ferromagnetic material separated from direct contact with the other core elements, each stator phase component thereby forming an autonomous electromagnet unit.
A plurality of motor control schemes are stored in memory. Subject to user or system selection, one of the motor control schemes is accessed from the memory by a controller for implementation. The controller generates control signals that are applied to energization circuitry for supplying current to the phase windings with a particular current waveform profile in accordance with the selected motor control scheme. The controller has an input terminal for receiving a user initiated torque command signal representing a desired motor torque. Each motor control scheme provides motor driving current that corresponds to torque command signals received at the controller input terminal. The controller has a second input terminal for receiving a user initiated selection command signal representing a stored motor control scheme, the controller accessing the corresponding motor control scheme from memory for implementation.
One of the stored motor control schemes may be a default scheme that is accessed by the controller from the memory in the absence of a signal received at the second controller input terminal. Preferably, the default motor control scheme corresponds to a current waveform profile, such as a substantially sinusoidal waveshape, which provides relative optimum operating efficiency. Another of the stored motor control schemes may provide a current waveform profile for maximum torque response, such as a substantially rectangular waveshape.
The energization circuitry may comprise a plurality of controllable switches, each phase winding connected respectively to one or more of the switches. A pulse width modulation conversion circuit may be connected to receive the control signals output from the controller to convert those signals to pulse width modulated signals that are applied to control terminals of the controllable switches. As an alternative, each stator phase winding may be connected to a power source via an amplifier having an input terminal coupled to the controller output.
The controller may have a plurality of inputs for receiving feedback signals representing various motor conditions. A current sensor preferably is coupled to each phase winding and connected to one of the controller inputs. Another controller input is coupled to receive rotor position signals produced by a rotor position sensor. Rotor speed signals may be received at another controller input. Each control scheme, when implemented, thus may be responsive to the current sensed in each phase winding, to rotor position and rotor speed.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.